Defect collecting structures for photolithography

ABSTRACT

A method and apparatus for collecting defect includes forming a defect collecting structure on a wafer such that any residue defects tend to settle on the defect collecting structure instead of the circuit patterns. The defect collecting structure can be located within the die or on the scribelines between the dies. When the defect collecting structure is located in a die, it should have dimensions significantly larger than the dimensions of the surrounding circuits patterns. 
     The defect collecting structure can include a plurality of defect collecting structures. The defect collecting structures can be contiguous or non-contiguous. The defect collecting structure(s) can occupy one hundredth of one percent of the die or more. 
     The defect collecting structures can be created on a wafer by coating, exposing, developing, and optionally, detecting defects. The wafer is exposed with a mask that includes a pattern for the defect collecting structure(s).

FIELD OF THE INVENTION

The present invention relates generally to manufacturing wafers withstructures that collect manufacturing defects. More specifically, itrelates to using portions of the wafer to attract particles that causedefects.

BACKGROUND OF THE INVENTION

During wafer fabrication of solid-state devices, photomasks, andreticles are used to form patterns for each layer of the devices on asemiconductor wafer. Even an extremely small defect created during thisprocess can greatly affect the production yield, circuit reliability, orcircuit functionality. Wafers are commonly inspected during each step ofthe fabrication process to detect such defects. Defects may becorrectable requiring additional time and expense before the fabricationprocess continues. Other defects may require scrapping the entire wafer.

Defects can occur in the resist development process. When resist isexposed, a chemical reaction occurs, which results in the production ofvarious chemical by-products. Some of these by-products are not readilysoluble in the developing solution, producing a residue that adheres tothe wafer surface. Thus, the residue can be difficult to remove andcreates defects. Such by-products tend to adhere to areas of the waferwith either relatively fewer patterns or to areas with large simplygeometric patterns. Photolithography resist residue causes such defectsand tends to adhere to such areas.

Residue defects adhering to the substrate in a large developed area caninterfere with subsequent fabrication steps including the etch andimplantation processes. Such interference can affect the performance oroperation of the device produced by the process. The residue defect canact as a partial mask causing incomplete etching of the underlying film.This leads to a defect that is subsequently covered by the film when thenext layer is applied during the manufacturing process. If this film isnon-opaque, the defect will be detected during subsequent defectinspections since the defect can be detected through opticallytransparent films. The residue defect adds to the resist thickness butstill prevents etching or implantation locally. Once the etch orimplantation process is complete, the defect is removed with the rest ofthe resist. Thus, a residue defect that adheres to a resist structurewill prevent a decrease in the signal-to-noise ratio at subsequentdefect inspections, relative to a residue defect that adheres to thesubstrate.

When the residue defect adheres to the a resist structure, it is lesslikely to interfere with subsequent etch or implantation processes.However, such a defect will decrease the signal-to-noise ratio for thedefect inspection at the photolithography layer.

“Lithography” is a process of transferring a pattern or image from onemedium to another, as from a mask to a wafer. Photolithography is alithographic technique involving light as the pattern transfer medium.

A “mask” is a transparent, for example glass or quartz, plate coveredwith patterns used in making integrated circuits. Each pattern consistsof opaque and transparent areas that define the size and shape of allcircuit and device elements. The mask is used to expose selected areasof resist, which defines areas to be etched. The term “reticle” includesmask, especially a photomask, used in wafer fabrication.

A “photoresist” is a light-sensitive liquid that is spread as a uniformthin film on a wafer or substrate. After baking to solidify the liquid,exposure of specific patterns is performed using a photomask. Materialremaining after development shields regions of the wafer from subsequentetch or implant operations.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, a wafer includes a substrate and aplurality of identical dies formed on the substrate. Each die contains afirst area and second area. The functional circuit pattern is in thefirst area and a defect collecting structure is in the second area. Thedefect collecting structure's surface area is at least four times largerthan the circuit patterns near the defect collecting structure. Thedefect collecting structure can be functional or non-functional,regularly or irregularly shaped. The defect collecting structure caninclude a plurality of defect collecting structures, they can becontiguous structures or non-contiguous. The defect collectingstructure(s) should occupy at least one hundredth of one percent (0.01%)of the die's surface area. Alternatively, the defect collectingstructure(s) can occupy at least one tenth of one percent (0.1%) of thedie's surface area or one percent (1.0%) of the die's surface area.

A standard wafer has a substrate and a plurality of dies formed on thesubstrate with scribelines separating the dies. A defect collectingstructure can be located on a scribeline. The defect collectingstructure attracts residue defects caused during die formation.

The method of manufacturing defect collecting structure on a waferincludes coating, exposing, developing, and optionally, detectingdefects. First, the wafer is coated with a resist. Second, the wafer isexposed with a mask. The mask can include a plurality of die regions.Each die region can include a first area that includes a circuitpattern. The mask can include a second area covering at least 0.1% ofthe die or at least 0.01%. The defect collecting structure pattern islocated in the second area. The first and second areas arenon-overlapping. Third, the resist is developed. Optionally, monitoredto detect defects on the wafer may be used.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The present invention is described with reference to the accompanyingfigures. In the figures, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the figure in which the reference numberfirst appears.

FIG. 1 is an illustration of a wafer with a plurality of dies and aclose view of a section of the wafer with fully removed resist;

FIG. 2 is an illustration of a cross-sectional view of the wafer of FIG.1;

FIG. 3 is an illustration of a wafer with a plurality of dies withdefect collecting structures in the dies;

FIG. 4 is an illustration of a cross-sectional view of the wafer of FIG.3;

FIG. 5 is an illustration of a wafer with a plurality of dies withdefect collecting structure on the scribelines; and

FIG. 6 is an illustration of a cross-sectional view of the wafer of FIG.5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a conventional wafer 100 with numerous dies 102. Each die102 includes a circuit pattern 110. The circuit pattern 110 has apattern dimension and performs functional tasks. The pattern dimensionis the resolution level of the fabrication technique used to create thecircuit pattern 110. For example, 2 to 3 micron circuit pattern 110 havebeen in uses for years. More recently, 1 micron and sub-micron circuitpattern 110 have become more common. The dies 102 are separated fromeach other with scribelines 104. Within each die 102 there can beresistless regions 106 where the resist has been fully removed. Aresidue defect 108 can occur anywhere on the wafer 100. Residue defectstend to occur in resistless areas such as resistless regions 106. Thewafer 100 may be made of silicon dioxide, metal film, or polysiliconcoated wafer.

FIG. 2 shows the wafer 100 of FIG. 1 is shown in cross-section afterdevelopment of the resist material. The wafer 100 includes a substrate202 and resist lines or circuit pattern 110. The wafer 100 may includeresidue defects 108. Such physical defects can affect the operability ofthe die 102. The residue defect 108 tends to adhere to a functional areaof the die 102 where the photoresist is completely removed. A residuedefect 108 in such an area is more prone to cause functional problemsthan if it had occurred elsewhere.

FIG. 3 shows a wafer 300 containing numerous dies 302 that are separatedfrom each other with scribelines 304. Within a die 302, there can beresist regions 308 and resist lines 310 where the resist has not beenremoved. Residue defect 306 may occur during the fabrication process.

Now, the resist region 308, also called defect collecting structures,can include a structure made of resist that is functional ornon-functional. The defect collecting structure 308 tends to attractresidue defects 306, thus preventing those residue defects 306 fromadhering to other areas of the die 302. Such structures 308 can belocated in areas of the die 302 that would otherwise have been fullydeveloped as unused portions of the die 302. The dimensions of thedefect collecting structure 308 should be sufficiently larger than thedimensions of the circuit patterns near the defect collecting structure302 so that the defect is attracted to the defect collecting structure308 and away from the circuit patterns. The defect collecting structure308 can be as small as 10 and as large as 100, or more times the size ofsurrounding circuit patterns. The defect collecting structure 308 can beas small as 0.01% of the die 302 surface area or larger. A larger defectcollecting structure 308 can be more effective at collecting defects306. A plurality of defect collecting structures 308 can be used on asingle die. The defect collecting structures 308 can be contiguous ornoncontiguous. The defect collecting structure 308 should be of asubstantially regular shape such as a rectangle, a circle, or atrapezoid. The defect collecting structure 308 can be a part of thefunctional circuit pattern of the die 302 or can be non-functional as acircuit component. The defect collecting structures 308 can be placed inthe die 302 such that each defect collecting structures 308 attractsdefects near it, protecting the circuit patterns on the entire die 302from defects.

It is preferred that the pattern dimension of the defect collectingstructure 308 be four times greater then the pattern dimension of thecircuit pattern 310. For example, if the circuit pattern 310 is a 1micron design, then the defect collecting structure 308 should be atleast 4 microns in width and length.

Referring to FIG. 4, a section of the wafer 300 of FIG. 3 is shown incross-section. The wafer 300 of FIG. 3 includes a substrate 402, resistlines 310, and a defect collecting structure 308. The wafer 300 mayinclude residue defects 306. Such physical defects can affect theoperability of the die 302.

Referring to FIG. 5, a wafer 500 containing numerous dies 502 that areseparated from each other with scribelines 504. The defect collectingstructure 510 can be located in the scribelines 504, thus notinterfering with the development of the die 502. The defect collectingstructure 510 attract residue defects 512 away from the dies 502.

Referring to FIG. 6, the wafer 500 of FIG. 5 is shown in cross-section.The wafer 500 of FIG. 6 includes a substrate 602, resist lines 508, anddefect collecting structures 510. The wafer 500 may include residuedefect(s) 512. The defect collecting structure 510 is in a scribeline504 and the residue defect 512 is on the defect collecting structure510.

While preferred embodiments have been shown and described, it will beunderstood that they are not intended to limit the disclosure, butrather it is intended to cover all modifications and alternative methodsand apparatuses falling within the spirit and scope of the invention asdefined in the appended claims or their equivalents.

What is claimed is:
 1. A semiconductor wafer comprising: (a) asubstrate; and (b) a plurality of identical dies formed on thesubstrate, each die containing first and second non-overlapping areas,the first area including a functional circuit pattern having a firstpattern dimension; the second area including a defect collectingstructure having a second pattern dimension at least four times thefirst dimension.
 2. The wafer of claim 1 wherein the defect collectingstructure is non-functional.
 3. The wafer of claim 1 wherein the defectcollecting structure is functional.
 4. The wafer of claim 1 wherein thedefect collecting structure is a regularly shaped, contiguous structure.5. The wafer of claim 1 wherein the defect collecting structure includesundeveloped resist material.
 6. The wafer of claim 1 wherein the secondarea includes a plurality of non-contiguous regions, each non-contiguousregion including a defect collecting structure.
 7. The wafer of claim 6wherein the second area occupies at least one hundredth of one percentof the die surface area.
 8. A semiconductor wafer comprising: (a) asubstrate; and (b) a plurality of dies formed on the substrate; (c)scribelines separating the dies; (d) a defect collecting structureattracting residue defects caused during development of photoresist, thedefect collecting structure being located within the scribelines.
 9. Thewafer of claim 8 wherein the scribelines include a plurality of defectcollecting structures.
 10. The wafer of claim 9 wherein the defectcollecting structures are non-contiguous.
 11. The wafer of claim 8wherein the defect collecting structures are non-functional.
 12. Thewafer of claim 8 wherein the defect collecting structures are aregularly shaped, contiguous structures.
 13. The wafer of claim 8wherein the defect collecting structures include undeveloped resistmaterial.